1. Field of the Invention
The invention relates to nanoparticles of chalcopyrites and methods of making the same. Invented chalcopyrite-based nanocrystalline or quantum dot materials may be important components of next-generation photovoltaic (PV) devices, for example, in solar cells that may feature greatly-increased solar-energy-conversion compared to conventional, silicon-based solar cell technology. The inclusion of nanocrystalline chalcopyrite semi-conductors according to embodiments of the invention may improve efficiency of photon conversion, for example, in quantum dot solar cells, may enable low-cost deposition of thin films, provide sites for exciton dissociation, and pathways for electron transport. Chalcopyrite quantum dots according to embodiments of the invention may be more resistant to degradation from electron, proton, and alpha particle radiation that the corresponding bulk materials, which resistance is a requirement of use in space solar cells. Embodiments of the invention provide rapid synthesis and size control methods for producing CuInS2, and other alloys thereof, semi-conductor nanoparticles using microwave irradiation.
2. Related Art
Since the 1970's with the widespread availability and use of the microwave oven, microwave irradiation has been tested for various uses in chemistry. Analytical chemistry has found microwave irradiation useful in determining the composition of petroleum, sediments, water, seaweed, and marine biological samples by digestion. Organic chemists have used microwave technology to assist in numerous chemical reactions since the publication of the forerunner articles in microwave-assisted organic reactions. Several key organic reactions such as organometallic, Michael, condensation, C—H bond activation, halogenation, nitration, macrocycle syntheses, coupling, ring-opening, alkylation, and acetylation reactions have seen dramatic increases in rate and efficiency using microwave-assisted techniques.
Growth of nanoparticles is highly dependent on the thermodynamic and kinetic barriers of the reaction. Conventional thermolysis relies on the conduction of blackbody radiation to drive the reaction, using the reaction vessel as an intermediary for the transfer of energy. This often causes sharp thermal gradients that create non-uniform thermal conditions resulting in non-uniform nucleation and particle growth.
Nanoparticles of the form Cu-III-VI2 have been made by the decomposition of single-source precursors (“SSPs”), solid-state reactions of the metal powders, and multiple-source precursors. Traditionally, the formation of the nanoparticles from SSP is facilitated by thermolysis of the precursor, although there have been reports of the nanoparticles formed by photolysis. Despite the potential benefits of replacing traditional thermolysis with microwave irradiation, only a few types of nanoparticles have been prepared via microwave radiation thus far, including CdSe, PbSe, Cu2-xSe, CuInTe2, and CuInSe2 nanoparticles from metal salts and CdSe, InP, and InGaP from respective SSPs.